1. Field of the Invention
The present invention relates to what is called a serial scan type inkjet printing apparatus that prints images using a print head that can eject ink, and a relevant ink jet printing method.
2. Description of the Related Art
A printing apparatus based on an ink jet method (hereinafter referred to as an “ink jet printing apparatus”) ejects ink from a print head onto a print medium for printing. The ink jet method allows definition to be increased more easily than the other printing methods. Furthermore, the ink jet printing apparatus advantageously operates fast and silently and is inexpensive. In particular, a demand for color image printing has recently been increasing, and ink jet printing apparatuses have been developed which can print high-quality images that are comparable to silver photographs. These printing apparatuses use a print head having a plurality of nozzles integrally arranged therein in order to improve print speed.
As an ink jet printing apparatuses of what is called the serial scan type, which prints images by moving a print head in a main scanning direction and conveying a print medium in a sub-scanning direction, an ink jet printing apparatus is known which adopts what is called a multi-pass printing method in order to print high-quality images. The multi-pass printing method completes an image in a predetermined print area by allowing the print head to perform a plurality of scans (a plurality of passes). During each of the scans, the print head ejects ink on the basis of print data shinned out by using a mask pattern. According to Japanese Patent Laid-Open No. 5-318770, mask patterns are prepared in association with the number of passes and are in an exclusively complementary relationship. If a print head is used which has a plurality of nozzle rows arranged in parallel and adjoined each other in the main scanning direction, each of the nozzle rows is associated with a plurality of mask patterns.
Furthermore, a known method of driving the plurality of nozzles forming each nozzle row is what is called a block driving method of dividing the nozzles into a plurality of blocks so as to vary a timing for ejecting ink among the blocks. The block driving method enables a reduction in the number of nozzles to be simultaneously driven and thus in a variation in driving voltage. The ink can thus be stably ejected. If a print head is used which has a plurality of nozzle rows arranged in parallel and adjoined in the main scanning direction, the nozzle rows are individually subjected to block driving.
With the ink jet printing apparatus based on the multi-pass printing method, the mask patterns are sequentially read from a specified address at an ink ejection timing when the nozzle rows in the print head moving in the main scanning direction are positioned over a print area on the print medium. For example, if a print head is used which has two nozzle rows arranged in parallel and adjoined in the main scanning direction, one of the nozzle rows is first positioned over the print area and the other is then positioned over the print area. Thus, reading timings for the mask patterns corresponding to the two nozzle rows are different from each other.
For example, it is assumed that with a 4-pass printing method in which each of the two nozzle rows uses four mask patterns A, B, C, and D, during the same print scan, one of the nozzle rows uses the mask pattern A, whereas the other uses the mask pattern B. If the timing for starting a read operation from the specified address is the same for the mask patterns A and B, the exclusively complementary relationship between the mask patterns A and B is maintained at every timing. However, if the timing for starting the read operation varies between the mask patterns A and B depending on the positions of the two nozzle rows, the exclusively complementary relationship between the mask patterns A and B may not be maintained at a certain timing.
With the ink jet printing apparatus based on such a multi-pass printing method, it is further assumed that the two nozzle rows are divided into the same number of blocks for block driving. In this case, provided that the exclusively complementary relationship between the mask patterns A and B is maintained at every timing, the nozzles in the nozzle rows which belong to the same driving block are not simultaneously driven. However, if the exclusively complementary relationship between the mask patterns A and B fails to be maintained at a certain timing, the nozzles in the nozzle rows which belong to the same driving block may be simultaneously driven.
Thus, with the printing apparatus using the print head that can eject ink through the plurality of nozzle rows, the combination of the multi-pass printing method and the block driving method may cause the nozzles in the nozzle rows which belong to the same driving block to be simultaneously driven. Thus, with an increase in the number of nozzles belonging to the same driving block and which are simultaneously driven, it may be impossible to make full use of the advantages of the block driving method.